Optical recording method

ABSTRACT

An optical recording method of recording information to a phase change optical recording medium with alternate application of peak power and bias power in a pulse manner and with changing a pulse application. interval continuously from an inner part through an outer part of the recording medium with an interval proportional to a window width Tw and a fixed interval, comprising the step of starting a top peak power application interval with a delay from a data input pulse signal starting time for a target mark length nTw, where n denotes an integer in a range between 3 and 14, with changing the delay in proportion to the window width Tw with changing a proportionality factor discretely with respect each linear velocity.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a recording method for a phase changeoptical recording medium, and, in particular, to a recording method fora rewritable DVD medium.

2. Description of the Related Art

Recently, a large size of image data is handled, and, therefore, arecording medium therefor thus having a larger storage capacity isdemanded. Further, it is also demanded to record such a large size ofimage data in the recording medium and reproduce the same therefrom athigh speed. A technique of phase change optical recording medium isapplied to a CD or DVD rewritable recording medium, and has been wideused since it has characteristics of having a large storage capacity andhas a high compatibility with a ROM. Especially, high speedrecording/playback has been achieved with CD-ROM or CD-R, and, as aresult, a phase change optical recording medium is also demanded to havea performance such that high speed recording/playback can be achievedtherewith. Furthermore, it is preferable that a disk which has aperformance of high speed recording/playback should also have acapability of recording thereto also with a low-speed disk drive whichis originally designed for a disk for a low recording linear velocity.In fact, a CD-R in the market has such a performance, thus covering awide range of recording linear velocity.

On the other hand, in order to achieve high speed recording, ahigh-power laser which can provide a higher peak power is needed.However, in general, an optical output of a laser mounted in a low-speeddisk drive is lower than the output of a high-speed disk drive.Therefore, it is difficult to achieve recording on a disk designed for ahigh linear velocity with a low linear velocity and with a lower powerin case a phase change optical recording medium is applied.

In case of applying a phase change optical recording medium, a mediumconfiguration is optimized so that recording at a high linear velocityis achieved. However, as a result, an optimum peak power increases evenin a case of recording at a low linear velocity same as in a case ofrecording at a high linear velocity. In order to achieve recording at alower linear velocity on a recording medium which is designed forrecording at a high linear velocity, it is necessary to improvesensitivity. For this purpose, there is a method in which thereflectance of a recording medium is decreased. However, in a case ofDVD, in order to provide a compatibility with a DVD-ROM, it is notpossible to lower the reflectance more than necessary. In a case of arewritable DVD, the maximum linear velocity is 2.4 time speed (2.4×) inthe market within recent several years, and, there is no backwardcompatible phase change optical recording medium such that recording canbe achieved thereon at a linear velocity higher than the above-mentionedmaximum linear velocity, and also, recording can be achieved thereonalso with a conventional disk drive designed merely for low linearvelocity recording.

In order to satisfy this requirement, it is necessary to find out arecording material and a medium configuration for a phase change opticalrecording medium on which recording can be achieved with a low power andalso having a wide margin of peak power, and to create an optimumrecording method therefor. As such a recording method, Japanese PatentNo. 2941703 discloses a method for forming a record mark in which a tailpulse bias power application ending time is determined without regard toa recording linear velocity. However, in this method, it may bedifficult to obtain satisfactory recording characteristics for a widerange of recording linear velocity.

Japanese laid-open patent application No. 2001-060319 discloses a methodin which a peak pulse power application interval and a subsequentmulti-pulse peak power application interval are changed according to arecording linear velocity, a bias power application interval is providedat the pulse tail, these intervals are optimized, and, thus,satisfactory recording characteristics can be obtained. However, thismethod does not include a method applicable for a CAV manner.

Further, Japanese laid-open patent application No. 2001-118245 disclosesa method based on the above-mentioned method which is applicable to aCAV (constant angular velocity) manner in which a recording linearvelocity changes continuously from a low linear velocity through a highlinear velocity as a recording radial position on the disk opticalrecording medium changes from an inner circumferential part through anouter circumferential part. In this method, a top peak power applicationstarting time is fixed, the peak power application interval is changed,and further a subsequent multi-pulse peak power application interval ischanged for each linear velocity in CAV recording. However, in thismethod, since a recording manner in which both the top pulse startingtime and the power application interval are changed is not applied, itmay not be possible to precisely control a starting position of a top ofa mark actually recorded.

Other than the above, the applicant of the present application proposedby Japanese patent application No. 2002-261281, a method applicable toCAV recording on a recording medium which is compatible inrecording/playback with a disk drive with a maximum linear velocity of2.4 time speed (2.4×).

However, in this method, control of a top peak power applicationstarting time may not be sufficient and thus there may occur a casewhere a satisfactory performance is not obtained for a certain item inrecording characteristics.

SUMMARY OF THE INVENTION

When a medium configuration and a recording material of a phase changeoptical recording medium are optimized for providing a medium suitablefor high linear velocity recording, it is difficult to obtain asatisfactory performance throughout a wide range of linear velocity onlyby means of pulse interval control of light pulse applied. However, auser who uses a medium wishes that the single medium covers a wide rangeof recording linear velocity so as to dispense him/her from replacingthe medium with another type of medium for each of different recordingline velocities. In order to satisfy this request, a recording methodshould be optimized by increasing the peak power applied, as one methodso as to achieve recording under such a condition.

However, according to a conventional method, unless control is madeprecisely for each of various recording line velocities on a top peakpower application starting time of pulse series to be applied uponrecording a predetermined length of mark on a recording medium,‘asymmetry’ which is an item of recording characteristics may not liewithin a required range. If so, recorded data thus obtained may not bereproduced properly therefrom, and, thus, data error may occur.Furthermore, along therewith, as a margin with respect to the peak powershould be narrowed, and, thus, recording signal quality may tend todecrease further.

An object of the present invention is to provide a recording method forrecording with a disk drive designed for CAV recording, and forrecording with accessing in a random manner at high speed on a phasechange optical recording medium on which recording can be achieved witha disk drive designed for a low recording linear velocity with a lowpeak laser power, also, recording can be achieved with a drive designedfor a high recording linear velocity.

Another object of the present invention is to provide a recording methodsuitable for CAV recording onto a phase change optical recording mediumon which recording at, a low linear velocity can be achieved in a lowpeak power range while recording at a high linear velocity can beachieved in a high peak power range, wherein, in the CAV recording, thelinear velocity changes continuously from the low linear velocitythrough the high linear velocity throughout a range from an innercircumferential part through an outer circumferential part of themedium. A further particular object of the present invention is toprovide a recording method advantageous for an optical recording mediumwhich is a rewritable DVD, having the maximum linear velocity of 4 timespeed (4×) of DVD, and, also, backward compatible with a disk drivewhich performs recording at a linear velocity in a range between 1 timespeed (1×) and 2.4 time speed (2.4×).

The above-mentioned objects can be achieved by the following firstthrough eighth aspects of the present invention:

According to the first aspect of the present invention, an opticalrecording method of recording information to a phase change opticalrecording medium utilizing change in optical constant caused byreversible phase change between a crystalline phase and an amorphousphase by controlling optical power to be applied to the recording mediumwith three values of peak power, erase power and bias power in arecordable range between a minimum linear velocity and a maximum linearvelocity, with alternate application of the peak power and bias power ina pulse manner and with changing the pulse application intervalcontinuously from an inner circumferential part through an outercircumferential part of the recording medium with an intervalproportional to a window width Tw and a fixed interval, includes thestep of:

a) starting a top peak power application interval with a delay from adata input pulse signal starting time for a target mark length nTw,where n denotes an integer in a range between 3 and 14, with changingthe delay in proportion to the window width Tw with changing aproportionality factor discretely with respect each linear velocity.

According to the second aspect of the present invention, in the opticalrecording method according to the above-mentioned first aspect of thepresent invention:

as the recording linear velocity is increased, with respect to those atthe minimum linear velocity, the top peak power application startingtime and a tail bias power application ending time are changed inproportion to the window width Tw with changing the proportionalityfactor for each linear velocity discretely.

According to the third aspect of the present invention, an opticalrecording method of recording information to a phase change opticalrecording medium utilizing change in optical constant caused byreversible phase change between a crystalline phase and an amorphousphase by controlling power to be applied to the recording medium withthree values of peak power, erase power and bias power in a recordablerange between a minimum linear velocity and a maximum linear velocity,with alternate application of the peak power and bias power in a pulsemanner and with changing the pulse application interval continuouslyfrom an inner circumferential part through an outer circumferential partof the recording medium with an interval proportional to a window widthTw and a fixed interval, includes the step of:

a) changing, upon increase in the recording linear velocity, a top peakpower application starting time and a tail bias power application endingtime in proportion to the window width Tw, with controlling any onethereof with an interval proportional to the window width Tw determinedby a fixed factor with respect to the window width Tw independent of thelinear velocity, with respect to those at the minimum linear velocity.

According to the fourth aspect of the present invention, the opticalrecording method according to any one of the above-mentioned firstthrough third aspects of the present invention includes the step of:

b) changing the tail bias power application ending time in a rangebetween 0 and the window width Tw upon decrease in the linear velocityin case where recording is made in a range between the maximum linearvelocity and the minimum linear velocity.

According to the fifth aspect of the present invention, in the opticalrecording method according to the above-mentioned fourth aspect of thepresent invention, the phase change optical recording medium applied ischaracterized in that, by continuously applying the erase power whichcorresponds to more than 20% of the maximum peak power used forrecording, the reflectance decreases from that of a not-yet-recordedstate at the maximum linear velocity, while the reflectance does notdecrease at the minimum linear velocity.

According to the sixth aspect of the present invention, in the opticalrecording method according to any one of the above-mentioned firstthrough fifth aspects of the present invention, the minimum linearvelocity is more than 1.0 times of a reference linear velocity, whilethe maximum linear velocity is four times the reference linear velocity.

According to the seventh aspect of the present invention, in the opticalrecording method according to any one of the above-mentioned firstthrough sixth aspects of the present invention:

the linear velocity for a case where CAV recording is performed within adata zone to be recorded is determined in a manner in which:

for a case where the linear velocity at the outermost radial position is4 time speed, the linear velocity at an intermediate radial position is2.83 time speed, and the linear velocity at the innermost radialposition is 1.65 time speed; and

for a case where the linear velocity at the outermost radial position is2.4 time speed, the linear velocity at the intermediate radial positionis 1.7 time speed, and the linear velocity at the innermost radialposition is 1 time speed.

According to the eighth aspect of the present invention, in the opticalrecording method according to any one of the above-mentioned firstthrough seventh aspects of the present invention, the linear velocitychanges continuously from the innermost radial position through theoutermost radial position while the window width is changed alongtherewith substantially in inverse proportion thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and further features of the present invention will becomemore apparent from the following detailed description when read inconjunction with the following accompanying drawings:

FIG. 1 shows a light emission waveform used for performingrecording/erasing onto an optical recording medium;

FIG. 2 illustrates an example of a basic configuration of an opticalrecording medium to which the present invention is applicable;

FIG. 3 shows a relation between the peak power and asymmetry in anembodiment 1 according to the present invention;

FIG. 4 shows a relation between the peak power and asymmetry in acomparative example 1;

FIG. 5 shows a relation between the linear velocity and jitter/asymmetryin an embodiment 2 according to the present invention;

FIG. 6 shows a dependency of a DOW-once jitter from a tail bias powerapplication ending time (dTera) in an embodiment 6 according to thepresent invention;

FIGS. 7 through 9 show pulse waveforms applied upon recording atrespective recording line velocities of 1.65× (1.65 time speed), 2.83×(2.83 time speed) and 4.0× (4 time speed) for each mark length in arange between 3T and 14T according to the embodiment 1; and

FIG. 10 shows comparison in mark shape between the embodiment 1 andcomparative example 1.

DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

According to the above-mentioned first aspect of the present invention,for example, a case is assumed where CAV recording is performed on anoptical recording medium with a diameter of 120 mm approximately fromthe innermost radial position of 24 mm through the outermost radialposition of 58 mm in a user data zone thereof. In this case, in eachpulse series of pulse application light, an interval for which a peakpower is applied is controlled according to a window width (Tw: 38.2nanoseconds for DVD's 1 time speed for example in case where recordingis performed at a uniform linear velocity) determined for each recordinglinear velocity. Especially, by controlling the peak power applicationtime at the top part of the pulse series according to the window width,it becomes possible to obtain satisfactory recording characteristicsthroughout a wide linear velocity range. Especially, this method isadvantageous for improving ‘asymmetry’. Furthermore, it becomes possibleto perform CAV recording with a further low peak power for a range oflinear velocity from the minimum recording linear velocity through anintermediate linear velocity.

The present invention according to the above-mentioned second and thirdaspects is methods which are advantageous for obtaining furthersatisfactory recording characteristics for a range from low linearvelocity recording in an inner circumferential recording zone throughouter high linear velocity recording in an outer circumferentialrecording zone.

The present invention according to the above-mentioned fourth and fifthaspects is methods which are superior in backward compatibility.

The present invention according to the above-mentioned sixth aspect ofthe present invention relates especially to a preferable recordinglinear velocity range. It is noted that the reference linear velocity ofDVD is 3.49 m/s.

A phase change optical recording medium for which the present inventionis applicable is one for which recording/playback can be performed witha laser beam in a range between 400 and 780 nm in wavelength. Forexample, in case of DVD, the wavelength of a laser applied is in a rangebetween 650 and 665 nm, with a numerical aperture of an objective lensapplied in a range between 0.60,through 0.65, an application beamdiameter of less than 1 μm, and the shortest mark length of 0.4 μm.

According to 1 time speed (1×) of DVD, the linear velocity isapproximately 3.5 m/s (3.49 m/s), and the clock frequency is 26.16 MHz(Tw: 38.2 nanoseconds). According to the 4 time speed (4×) of DVD, thelinear velocity is approximately 14 m/s (13.96 m/s) and the clockfrequency is 104.6 MHz (Tw: 9.56 nanoseconds).

According to the present invention, a case is assumed in which CAVrecording is performed onto an optical recording medium which is optimumfor a maximum recording linear velocity of 14 m/s in a rangeapproximately from the innermost radial position of 24 mm at recordingbeginning through the outermost radial position of 58 mm in a diameterof 120 mm. In this case, CAV recording is performed in two types oflinear velocity ranges, i.e., a first range from 1.65 time speed through4 time speed (intermediate linear velocity: 2.83 time speed) and asecond range from 1 time speed through 2.4 time speed.

The optical recording medium to which the present invention isapplicable has these features, and also, in order to obtain satisfactoryperformance by means of a recording method, the following light emissionwaveform is applied:

FIG. 1 shows a light emission waveform applied for recording/erasingaccording to the present invention. As a light application power, a peakpower (Pp), an erase power (Pe), and a bias power (Pb) are used. Asshown, a top peak power (heating pulse) application interval Ttop for atop pulse, an intermediate peak power (heating pulse) applicationinterval Tmp for an intermediate pulse and a tail peak power (heatingpulse) application interval Tmp for a tail pulse, for each of which apeak power Pp is applied for hearting a recording layer of the opticalrecording medium, are set. Furthermore, a bias power (cooling pulse)application intervals Tb1, Tb2 and Tb3 for applying the bias power Pbare also set. As shown, for an intermediate window width Tw, the sum ofthe intermediate peak power application interval Tmp and the bias powerapplication interval Tb2 is equal to the Tw. Actually, the total numberof the pulses are (n-1) or (n-2) with respect to a desired mark lengthnT where n lies within a range between 3 and 14. In case where n is morethan 3, the number of intermediate peak power application intervals Tmpincreases accordingly together with the respective bias powerapplication intervals Tb2 as shown in FIGS. 7, 8 and 9, for example.

In order to perform CAV recording, the peak power application intervalis controlled for each linear velocity with an interval proportional tothe window width Tw corresponding to particular linear velocity and afixed interval. Thus, a control is made in proportion to the windowwidth Tw. Thereby, in comparison to a case where the interval is fixed,it becomes possible to continuously change the actual peak powerapplication interval according,to change in the linear velocity.Thereby, recording can be achieved in a condition without changing thepulse interval discontinuously from a certain intermediate linearvelocity.

Conventionally, in case of recording in a range between 1 time speed and2.4 time speed, it is possible to form an optimum mark by, other thanemploying a control in which the peak power application interval iscontrolled with a sum of an interval proportional to the window width Twand a fixed interval, instead employing a control in which the peakpower application starting time on the top pulse is fixed without regardto the linear velocity while the bias power application ending time onthe last pulse is changed according to the linear velocity.

However, in case of applying a recording medium designed both for 4 timespeed recording and for backward compatibility, even when this methodcan be applied as it is for a range in linear velocity from 1.65 timespeed through 4 time speed, a satisfactory performance may not beobtained in CAV recording. This is because, when the peak powerapplication starting time on the top pulse is determined suitable for 4time speed recording, there is a tendency in which, in a range of alower linear velocity, a short mark becomes shorter than a predeterminedmark length. Thereby, a playback error may be likely to occur for such ashort record mark.

In comparison thereto, according to the present invention, the peakpower application starting time dTtop shown in FIG. 1 is controlled sothat it changes in proportion to the window width Tw and also theproportional part changes continuously with respect to the linearvelocity applied. Thereby, satisfactory performance can be obtainedthroughout a range between the low linear velocity and the high linearvelocity. Furthermore, in this case, it is preferable that, a control ismade such that, for the low linear velocity range, the peak powerapplication starting time on the top pulse is made earlier than thebeginning reference time (ta in FIG. 1), while the same is made laterthan the beginning reference time ta as the linear velocity rangebecomes higher, continuously.

Simultaneously, the part proportional to the window width Tw in the tailbias power application interval is changed continuously in the followingmanner: The tail bias power application ending time is made later than areference position (tb in FIG. 1) so that the tail bias powerapplication interval Tb3 becomes longer for the lower linear velocityrange while the same is made earlier; than the reference position (tb)so that the tail bias power application interval Tb3 becomes shorter.Thus, the tail bias power application ending time varies continuously asthe linear velocity applied varies. This recording method is optimum forthe recording medium which the present invention is applicable.Especially, for the 4 time speed recording which is recording at thehighest linear velocity, it is preferable that the tail bias powerapplication interval Tb3 is made to be 0 or to close to 0 unlimitedly,while the same is made to have an interval approximately equal to thewindow width Tw for a lower linear velocity range, especially, for 1time speed as shown in FIGS. 7, 8 and 9. A range of linear velocitywhich is especially advantageous to be applied in the above-mentionedmethod is a range between 1.65 time speed (1.65×) and 4 time speed (4×).

The factor of proportionality with respect to the window width Tw isdetermined from an interval controllable in a recording apparatusapplied in case of 4 time speed recording. For example, in case aninterval of 0.5 nanoseconds is the minimum controllable interval by theapparatus,9.56 (nanoseconds)×c=0.5 (nanoseconds), and thus,c≈1/20=0.05.Thus, Tw/20 is the minimum controllable time interval. Accordingly,depending on a particular type of recording medium, a factor ‘i’ isdetermined as being 1, 2, 3, . . . , and control of the relevantinterval (dTtop or dTera) is made by applying the value (i×Tw/20) as theabove-mentioned interval proportional to Tw.

On the other hand, same as the above, the above-mentioned fixed intervalof the interval (dTtop or dTera) is also determined from an intervalcontrollable in the recording apparatus applied so that the relevantpulse interval can be controlled continuously according to the linearvelocity. Assuming that the interval of 0.5 nanoseconds is the minimumcontrollable interval, a control of the fixed interval is made byapplying thereto an internal (0.5×j) where j=1, 2, 3 . . . . As aresult, the heating pulse interval is expressed by the following formulawith the interval proportional to the window width Tw (i×(Tw/20) and thefixed interval (0.5j):i×(Tw/20)+0.5j.Thereby, as the recording linear velocity varies, Tw determinedcorresponding to the linear velocity varies accordingly, and thus, CAVrecording is achieved.

Furthermore, it is also possible to perform a control such that the toppeak power application interval Ttop is made different from theintermediate or tail peak power application interval Tmp. That is,Ttop≠Tmp. It is preferable that a time interval of the Ttop or Tmp lieswithin a range between 0.2×Tw and 0.8×Tw.

Assuming that c= 1/16, dTtop=i×(Tw/16), and a range later from thereference position ta is expressed by minus (−) while a range earlierfrom the reference position ta is expressed by plus (+), it ispreferable that dTtop is −(3×Tw/16) for 4 time speed; dTtop is (3×Tw/16)for 1.65 time speed; and dTtop is (0×Tw/16) for the intermediate linearvelocity of 2.83 time speed, for example. As the proportionality factorvaries linearly in this case, CAV recording is achieved therewith.

Similarly, as to the tail bias power ending time dTera mentioned above,assuming that a range earlier from the reference position tb isexpressed by plus (+) while a range later from the reference positiontb, i.e., a range in which the bias power application interval Tb3becomes longer, is expressed by minus (−) it is preferable that thedTera for 4 time speed, 2.83 time speed and 1.65 time speed is, in thestated order, +(8Tw/16), +(2Tw/16) and +0, respectively.

It is preferable that dTtop lies within a range between −0.5 and 1 Tw,and, more preferably, within a range between −0.25 and 0.5 Tw.

It is preferable that dTera lies within a range between −0.1 and +0.7Tw, and, more preferably, within a range between −0.5 and +0.6 Tw.

By thus adjusting the light emission pulse intervals, it is possible toobtain satisfactory recording characteristics.

The peak power Pp, erase power Pe and bias power Pb are maximum 22 mW,12 mW and 1 mW, respectively, on the disk surface. Also in a case ofperforming CAV recording with a backward recording/playback apparatushaving a maximum linear velocity of 8.5 m/s and a maximum peak power of16 mW, the same method is applied.

Requirements to be satisfied by an optical recording medium which issuitable to the above-mentioned recording method and also on whichrecording can be achieved for a wide range of linear velocity betweenthe low linear velocity and the high linear velocity are as follows: Bycontinuously applying the erase power which is more than 20% of themaximum peak power for recording, the reflectance of the recordingmedium drops from that in the not-yet-recorded state at the highestlinear velocity, while, the reflectance at least does not drop at thelowest linear velocity from that in the not-yet-recorded state.

In case where the peak power is maximum 22 mW, an optical recordingmedium which is applicable by the present invention has the reflectancereduced from that of the not-yet-recorded state at the linear velocitynot less than a range between 8 and 11 m/s after continuous applicationof the erase power of 11 mW, which is 50% of the maximum peak power of22 mW. A preferable linear velocity range in which the reflectancestarts dropping is a range between 9.5 and 11 m/s. On the other hand, incase where the recording linear velocity is 14 m/s, the reflectancedrops by 30 through 70% from that of the not-yet-recorded state. On theother hand, in case of linear velocity of 3.5 m/s, the reflectancebecomes equal to or higher than that of the not-yet-recorded state.Thereby, it becomes possible that, in the optical recording medium whichsatisfies the above-mentioned requirements, recording can be performedwith a low peak power in a low recording linear velocity range, and,also, recording can be performed also in a high linear velocity range.

FIG. 2 shows one example of a basic layer configuration of an opticalrecording medium to which the present invention is applicable. As shown,on a substrate 1, a lower protective layer 2, an interface layer 7, aphase change recording layer 3 which reversibly changes in phase betweena crystalline phase and an amorphous phase, an upper protective layer 4,a sulfating-avoiding layer 5, and a reflective layer 6 are laminated inthe stated order. The interface layer is provided if necessary, and itmay also be provided between the recording layer and upper protectivelayer.

As material of the substrate, a plastic such as polycarbonate (PC),polymethylmethacrylate acid (PMMA) or so, or a glass, which istransparent with respect to recording/playback light applied is used.

As material of the upper and lower protective layers, any one of varioustypes of dielectric materials may be used. For example, metal oxide suchas SiOx, ZnO, SnO₂, Al₂O₃, TiO₂, In₂O₃, MgO, ZrO₂, Ta₂O₅ and so forth;nitride'such as Si₃N₄, AlN, TiN, BN, ZrN, and so forth; and sulfide suchas ZnS, TaS₄ and so forth; and carbide such as SiC, TaC, B₄C, WC, TiC,ZrC and so forth, can be cited as candidates for this material.

Each of these materials may be applied alone or some thereof may beapplied as a composite. Especially, a composite of ZnS and SiO₂ iscommonly used in a phase change optical recording medium, and, in thiscase, the mixture ratio thereof is preferably 80:20 (molar ratio).

As a material of the lower protective layer, a material which has a lowthermal conductivity and a low specific heat, which is not likely to becrystallized by overwriting operation, and which does not have crackoccurrence, element diffusion or so, even having undergoing a history ofmany times of heating and rapid cooling, is preferable. ZnS.SiO₂ (80:20)satisfies these requirements, and, thus, may be preferably used also asthe upper protective layer.

Also, ZrO₂ containing Y₂O₃ in a range between 3 and 6 molar % has arefractive index equal to or more than that of ZnS.SiO₂, and, thus, isalso preferable for the same purpose. In case of ZrO₃ is applied alone,a record mark is likely to be degraded due to crystallization when beingleft in a high temperature environment.

A composite of ZrO₂.Y₂O₃ (3 molar %) and TiO₂ is also preferable. Themixture ratio of 20:80 (molar ratio) is preferable in this case.However, other than this ratio, the mixing amount of TiO₂ should be 70molar % at most. In case of TiO₂ alone, stability as an oxide film isnot satisfactory, and it is likely to react with a constituent of therecording layer.

As the oxide, Al₂O₂ is also preferable.

The interface layer is provided for the purpose of facilitating crystalgrowth at a record mark end part, increasing the erasure ratio, andthus, improving overwriting performance. It is found out that the filmthickness thereof should lie within a range between 1 and 5 nm, so thatthe material provides a required performance, and also, degradation inpreservation reliability can be reduced fairly.

The film thickness of the lower protective layer should lie within arange between 40 and 250 nm, and, preferably within a range between 45and 80 nm. If the thickness is smaller than 40 nm, environmentalresistance function may be degraded, radiation function may be degraded,and repetitive overwriting performance may be degraded. If the thicknessis larger than 250 nm, film peeling off, or crack generation may occurdue to temperature rise in the film during a film formation process in aspattering method or so.

The film thickness of the upper protective layer should lie within arange between 5 and 50 nm, and preferably, within a range between 8 and20 nm. If it is larger than 50 nm, repetitive overwriting performancemay be degraded due to deformation by temperature rise or degradation inradiation performance.

As the reflective layer, any metal materials such as Al, Ag, Cu, Pd, Cr,Ti or so may be used alone or in a form of an alloy thereof. Especially,Ag or an Ag alloy which has a high thermal conductivity is preferable.

However, in case of employing Ag or an Ag alloy, the sulfating-avoidinglayer should be provided between the reflective layer and the upperprotective layer for the purpose of avoiding corrosion of Ag by sulfurincluded in the upper protective layer. As the material of thesulfating-avoiding layer, it is found out from a study until now that Siand SiC are preferable. ZrO₂, MgO, TiOx are also suitable for thispurpose.

In case of SiC, the effect is still high even if the film thickness isreduced to the order of 3 nm. However, at least 2 nm is needed, and theupper limit is 10 nm. If the film is made thicker than this upper limit,the distance from the reflective layer becomes larger, and, as a result,the radiation efficiency is degraded, and, also, the reflectance becomesdegraded due to high absorption.

The thickness of the reflective layer is preferably within a rangebetween 50 and 250 nm. If the film thickness is too large, while theradiation performance is improved, deformation may occur in thesubstrate due to temperature rise in the medium during film formationprocess. If the thickness is too small, the radiation performance isdegraded, and thus, the recording characteristics are degraded.

As the phase change recording layer, until now, based on eutecticcomposition around Sb₇₀Te₃₀, Ag, In and further Ge are added thereto,and, thus, a AgInSbTe family and a AgInSbTeGe family have been used,since they are materials suitable for high recording linear velocity andalso high density recording. As the ratio of Sb with respect to Teincreases, the crystallization speed increases. However, as the amountof Sb exceeds 80 atomic %, the crystallization speed increases, whilethe preservation performance becomes extremely worse, and also, itbecomes difficult to form an amorphous phase. Accordingly, thepreferable amount of Sb to achieve high linear velocity recording iswithin a range between 65 and 80 atomic %. On the other hand, the amountof Te should be within a range between 15 and 25 atomic %.

Ge is an essential element for the purpose of improving the preservationperformance of a record mark under high temperature environment. It isconsidered that, the bond energy between Ge and Te is large, also, thecrystallization temperature increases as the Ge adding amount increases,and thus, the preservation performance is improved. However, if the Geis added too much, the crystallization temperature increases further,and thus, the crystallization speed decreases. Accordingly, the Geadding amount should preferably be not more than 5 atomic %.

Ag stabilizes a record mark, and does not have a function to increasethe crystallization temperature much. However, if Ag is added too much,the crystallization speed is lowered, and, thus, it is not preferable toadd Ag too much. Accordingly, the adding amount of Ag is preferably notmore than 3 atomic %.

In increases the crystallization speed and also increases thecrystallization temperature. Accordingly, the preservation performanceis increased therewith. However, if it is added much, demixing is likelyto occur, and thus repetitive overwriting performance may be degradedand also degradation against playback light power may occur. Accordinglythe adding amount thereof should be not more than 5 atomic %.

Other than In, Ga or Mn also increases the crystallization speed. Ga hasa performance of increasing the crystallization speed more than that ofIn in the same amount. However, the crystallization temperature is alsoincreased. Accordingly, it is preferable to add Ga in a range not morethan 5 atomic %. On the other hand, as to Mn, it is sufficient to add 5atomic % at most. By further adding Ga, it is possible to improve thecrystallization speed and preservation performance effectively.

The thickness of the phase change recording layer is preferably in arange between 10 and 20 nm. If it is thinner than 10 nm, a difference inreflectance between crystalline phase and amorphous phase is reduced,while, if it is thicker than 20 nm, the recording sensitivity and therepetitive overwriting performance become worse.

Consequently, a preferable thickness of each layer of the phase changeoptical recording medium which the present invention is applicable is asfollows:

the interface layer: in a range between 2 and 4 nm;

the phase change recording medium: in a range between 11 and 13 nm;

the upper protective layer: in a range between 10 and 15 nm;

the sulfating-avoiding layer: in a range between 3 and 5 nm; and

the Ag reflective layer: in a range between 120 and 160 nm.

In this case, the film thickness of the lower protective layer ispreferably within a range between 40 and 80 nm, especially thereflectance becomes lowest around 50 nm thereof, and the performancebecomes satisfactory especially within a range between ±5 nm of thisfilm thickness.

The substrate is made such that the pitch between adjacent grooves inwhich record marks are written is 0.74 μm; the groove depth is in arange between 15 and 45 nm; and the groove width is in a range between0.2 and 0.3 μm. The groove is a wobbling groove having the cycle ofapproximately 820 kHz. In an address part, a phase in the frequency ofthe wobbling groove is modulated, the change in the phase is detected,the detected signal is converted into a binary signal, and thus, aparticular address is read therefrom. The amplitude of the wobbling partis in a range between 5 and 20 nm. A recording line density is 0.267μm/bit, and recording is performed according to an (8-16) modulationmethod.

Specific embodiments of the present invention will now be described indetail. However, the present invention is not limited to theseembodiments.

Embodiment 1

First, a phase change optical recording medium was produced as follows:

By using a substrate made of polycarbonate with a thickness of 0.6 mm,having a groove pitch of 0.74 μm, a groove width of 0.25 μm and a groovedepth of 25 nm for recording record marks therein, each layer waslaminated thereon by a spattering method.

First, a target of ZnS:SiO₂=80:20 (molar %) was used, and a lowerprotective layer with a film thickness of 54 nm was provided.

Then, a target of a composition of Ge:Ag:In:Sb:Te=3.8:0.3:3.5:72:20.4was used, and a phase change recording layer with a film thickness of 12nm was provided.

Then, a target of composite oxide of ZrO₂.Y₂O₃ (3 molar %)·TiO₂ (20molar %) was used, and an interface layer with a film thickness of 3 nmwas provided.

Then, a target of ZnS:SiO₂=80:20 (molar %) was used, and an upperprotective layer with a film thickness of 11 nm was provided.

Then, after an SiC layer (sulfating-avoiding layer) with a filmthickness of 4 nm and an Ag reflective layer with a film thickness of140 nm were provided, SD318 ultraviolet curing resin made of DainipponInk Co. Ltd. was coated thereon with a thickness of 5 μm for the purposeof improving environment-resistance property, then curing thereof wasachieved, and, thus, an environment-resistance protective film wasformed.

Finally, the thus produced substrate with the respective layers thusprovided thereon as mentioned above and another substrate same as theabove-mentioned substrate but having no layers formed thereon were madeto adhere together with a use of ultraviolet curing resin (made ofacryl, by Nippon Kayaku Co., Ltd., DVD003) with a thickness of 40 Mm,and, thus, the phase change optical recording medium was obtained.

After that, by using a large diameter LD (with a beam diameter of 1 μmalong track direction×75 μm along radial direction) with a wavelength of810 nm, the recording layer was crystallized (initialized) at a linearvelocity of 10 m/s, with power of 1300 mW, at a head feeding speed of 36Mm/rotation.

Then, when DC light of 11 mW was applied to this optical recordingmedium with the above-mentioned recording head while the linear velocitywas changed, the reflectance started dropping from around the linearvelocity of 10 m/s. In other words, after the DC light application wasperformed upon changing the linear velocity, the reflectance thereof wasmeasured for each position at which the DC light application was thusmade at a different linear velocity. Thereby, it was found out from themeasurement result that the reflectance started dropping from around thelinear velocity of 10 m/s as mentioned above. By this measurement, thecrystallization speed of the recording medium was measured.

Recording/playback was performed with a pickup head with a wavelength of662 nm and an objective lens of NA: 0.65 so that the recording densityof 0.267 μm/bit was obtained at the maximum linear velocity of 14 m/s.The recording was performed in a condition where the peak power wasmaximum 21 mW, the bias power was 5 mW, and the erase power lay within arange between 30% and 55% of the peak power. The number of pulses foreach mark length was n-1 where n lay within a range between 3 and 14.The optimum power for each recording linear velocity was set as being18.5 mW, 18.5 mW and 19.5 mW for 1.65 time speed (1.65×), 2.83 timespeed (2.83×) and 4.0 time speed (4.0×), respectively.

The following Table 1 shows recording conditions under which CAVrecording was performed within a range of linear velocity between 14m/s. (4 time speed) and 5.8 m/s (1.65 time speed). Parameters shown inTable 1 are basically same as the symbols shown in FIG. 1. In addition,it is noted that Ttop≡OP1, Tmp≡(OPj, OPm) and ε=Pe/Pp. TABLE 1 recordinglinear recording velocity linear (time velocity Parameter speed) (m/s)dTtop Ttop Tmp dTera ε 1.65 5.8 3 × Tw/ 7 × Tw/ 5 × Tw/ 0 0.53 16 16 +16 + 1.2 ns 1.8 ns 2.83 9.9 1 × Tw/ 2 × Tw/ 0.50 16 16 4.00 14.0 −2 ×Tw/ 8 × Tw/ 0.31 16 16

By determining the pulse intervals as shown in Table 1, and controllingthe pulse beginning times and ending times with the values of dTtop anddTera, satisfactory performance could be obtained. Especially, byadjusting the beginning time of the top pulse (peak power starting timeat the pulse top), and also, changing this value linearly within a rangebetween the minimum linear velocity at the inner circumferential partand the maximum linear velocity at the outer circumferential part of arecording data zone of the optical recording medium, the performance inCAV recording was improved in comparison to a conventional case wherethe above-mentioned value was fixed.

Further especially, the following advantages of the present inventionwere proved: It is preferable that a reflectance which is a half of adifference between a reflectance on a shortest mark (amorphous phase)and a reflectance on a position (crystalline phase) between the adjacentmarks is made equal to a reflectance which is a half of a differencebetween a reflectance on a longest mark (amorphous phase) and areflectance on a position between the adjacent marks, which valueaffects a playback signal, and is used for evaluation as an item called‘asymmetry’ of reproduced signal characteristics. Even when othercharacteristics are satisfactory, the value of asymmetry has a largeinfluence on the reproduced signal error. The above-mentioned control ofdTtop according to the present invention is advantageous for controllingthis value of asymmetry to effectively make it to lie within a rangebetween 0 and 5% at any linear velocity. In the embodiment 1 describedabove, as shown in FIG. 3, the asymmetry falls approximately at zeroregardless of the linear velocity. Furthermore, for each linearvelocity, the jitter falls within 9% up to a thousand times ofoverwriting.

FIGS. 7 through 9 show pulse waveforms applied when recording is made atrespective recording line velocities of 1.65× (1.65 time speed), 2.83×(2.83 time speed) and 4.0× (4 time speed) for each mark length in arange between 3T and 14T according to the embodiment 1 described above.

COMPARATIVE EXAMPLE 1

For the purpose of comparison with the above-mentioned embodiment 1,dTtop was fixed at a value determined for 4 time speed recording, andrecording was performed at 2.83 time speed and 1.65 time speed with thefixed dTtop in a comparative example 1. The results are shown in FIG. 4.

As shown in FIG. 4, as the recording speed was changed without changingdTtop, the asymmetry became smaller than −5% (−0.05) in a low linearvelocity range. As a result, the data error rate is likely to increaseupon playback in this range. FIG. 10 show 3T marks obtained from theabove-mentioned embodiment 1 and the comparative example 1 for thepurpose of comparison. As can be seen therefrom, especially in case offixing the top starting time at a value for the conditions of 4× asmentioned above in the comparison example 1, the mark length isshortened in a low linear velocity range, the total length of the markis thus shortened, and thus, the jitter and asymmetry become worse.Further, on the contrary, when the interval (controlled with dTera) forwhich the bias power is applied at the tail part is fixed at a value forthe conditions of 1.65×, the mark tail part in case of 4× recording ismuch elongated, and, thus, the mark is elongated backward especially atthe centre of the groove.

Embodiment 2

By using the optical recording medium same as that in theabove-mentioned embodiment 1, recording/playback was performed under theconditions shown in Table 2 below. The other conditions were same asthose in the embodiment 1. The maximum linear velocity was 2.40 timespeed (8.4 m/s), the minimum linear velocity was 1.0 time speed (3.5m/s) and the intermediate linear velocity was 1.7 time speed (6 m/s).TABLE 2 recording linear recording velocity linear (time velocityParameter speed) (m/s) dTtop Ttop Tmp dTera ε 1.0 3.5 Tw/6 Tw/6 + Tw/6 +6 ns −Tw/6 0.47 6 ns 1.7 6 Tw/6 0 0.50 2.40 8.4 Tw/6 Tw/6 0.53

FIG. 5 shows a result of evaluation of jitter and asymmetry in therecording characteristics thus obtained with the peak power of 15 mW. Asshown, satisfactory characteristics were obtained approximately withoutdepending on the linear velocity. In the above-mentioned linear velocityrange, the top pulse beginning time (peak power application startingtime of the pulse top: dTtop) was determined by a fixed factor (⅙) withrespect to the window width Tw without regard to the linear velocity.The jitter shown in FIG. 5 is a result obtained at a tenth of directoverwriting (DOW).

Embodiments 3 through 5

In an embodiment 4 of the present invention, by using the same opticalrecording medium as that in the above-mentioned embodiment 1, when thelinear velocity was changed from 3.5 m/s through maximum 14 m/s at arate of 0.5 m/s; the linear velocity at which the reflectance starteddropping was around 10.5 m/s (see the embodiment 4 in Table 3 below).

Then, optical recording media were produced in the same way as that inthe embodiment 1 except that the material of the recording layer waschanged to compositions of Ag:In:Sb:Te:Ge=0.5:5:68:24.5:2 (embodiment 3of the present invention) and Ag:In:Sb:Te:Ge=0.3:4:73:19.7:3 (embodiment5 of the present invention), respectively. Then, when measurement wasperformed as in the embodiment 4 described above, the reflectancestarted dropping around 8.5 m/s and 11.5 m/s for the embodiments 3 and5, respectively, as shown in Table 3. TABLE 3 reflectance dropping DOW 1jitter (%) start linear 2.4 time velocity 4 time speed speed embodiment3  8.5 m/s 10.2 7.5 embodiment 4 10.5 m/s 8.3 7.9 embodiment 5 11.5 m/s9.4 8.5

For each recording medium, recording was performed with the peak powerof 15 mW at 2.4 time speed and 19 mW at 4 time speed. After that, DOWonce jitter (the jitter obtained after once of direct overwriting) wasmeasured. As a result, less than 9% was obtained for each linearvelocity only in the embodiment 4 as shown in Table 3.

The peak power of an evaluation apparatus used for these embodiments ismaximum 21 mW, and the erase power which is approximately 50% of thepeak power was used. Thus, it was found out that, especially, in aconfiguration by which both the characteristics obtained at 2.4 timespeed with less than 15 mW and those obtained at 4 time speed weresatisfactory, the linear velocity at which the reflectance startsdropping was around a range between 10 and 11 m/s.

Embodiment 6

With a use of the optical recording medium same as that in theabove-mentioned embodiment 1, and recording/playback was performed under4 time speed recording conditions same as those shown in Table 1 exceptthat dTera was changed therefrom. FIG. 6 shows a dependency from thebias power application ending time at the tail part (dTera) of the DOWonce jitter. dTera is expressed as a plus (+) value in a range in whichthe tail bias power application ending time is earlier than thereference point tb shown in FIG. 1 while expressed as a minus (−) valuein a range in which the tail bias power application ending time is laterthan the reference point tb shown in FIG. 1. The horizontal axis of FIG.6 shows dTera=k×(Tw/16), and the graduations on the horizontal axisdenote the values of ‘k’.

As can be seen from FIG. 6, as the bias power application ending timeapproximates the value of 8Tw/16 (k=8), in other words, as the biaspower application interval Tb3 approximates zero, satisfactorycharacteristics of jitter of less than 9% are obtained.

Embodiment 7

Other than the material of the recording layer, the conditions of theconfiguration, materials and film thickness were same as those in theembodiment 1, and an optical recording medium was produced in the samemethod as that in the embodiment 1. The recording material had thecomposition ratio of Ge:In:Sb:Te=3.5:3.5:72.5:20.5.

After that, by using a large diameter LD (with a beam diameter of 1 μmalong track direction×75 μm along radial direction) with a wavelength of810 nm, the recording layer was crystallized (initialized) at a linearvelocity of 10 m/s, with power of 1300 mW, and head feeding speed of 36μm/rotation. Then, upon applying DC light of 11 mW to the recordingmedium while changing the linear velocity, the reflectance starteddropping around the linear velocity of 10.5 m/s. Recording was performedwith recording power under the same conditions as those shown in Table 1of the embodiment 1. As a result, the same recording characteristics asthose in the embodiment 1 were obtained.

By adjusting the reflectance dropping start linear velocity (the linearvelocity at which the reflectance starts dropping) toward around a rangebetween 10 and 10.5 m/s, in other words, by optimizing thecrystallization speed toward a certain limited range, according to themethod described above, 4 time speed recording was properly performed ina CAV manner, and, also, satisfactory recording characteristics wereobtained even when recording was performed with low power at a recordingspeed in a range between 1 and 2.4 time speed.

The upper limit of the recording power described in a document entitledby DVD+RW ver. 1.1 is 15 mW, and, also according to the presentinvention, satisfactory characteristics were obtained with power lessthan 15 mW in a range between 1 and 2.4 time speed. Accordingly, it canbe said that backward drive compatibility is provided. It is preferableto set the crystallization speed of the recording medium, i.e., a speedin erasing a record mark (crystallization), by setting the reflectancedropping start linear velocity of the recording medium into around 3time speed (10.5 m/s) which is higher than the intermediate linearvelocity (2.5×) of the recording linear velocity range between 1 and 4time speed, at which the embodiment of the present invention providedthe especially high advantage as mentioned above for the embodiment 4.Thereby, it is possible to perform recording even for a range between 1and 4 time speed in conditions (recording power and laser light emissionwaveform) completely same as those in which recording is made in a rangebetween 1 and 2.4 time speed according to the conventional way (DVD+RWbook, ver. 1.1).

On the other hand, in order to perform recording at 4 time speed (DVD+RWbook, ver. 1.2), a design is made for decelerating the crystallizationspeed, degradation in the factors of jitter, asymmetry, reflectancedrop, and modulation drop thereby become remarkable, and thus, therecording characteristics becomes much worse as the number of times ofoverwriting increases, according to the conventional method. In contrastthereto, by using the recording medium configuration applicable in thepresent invention described above, and also, by controlling the lightemission waveform in recording, in particular, by controlling the peakpower application starting time and application interval at the toppart, and the bias power application interval at the tail part accordingto the present invention described above, it becomes possible to achievenot only CLV recording at 4 time speed but also CAV recording in a rangebetween 1.65 time speed and 4 time speed. To control the pulse at thetop part and tail part means to control the length at the top part andtail part of a record mark, and, by such a control according to thepresent invention, these parts are accurately controlled in the requiredconditions.

Thus, by applying the present invention, it is possible to providebackward compatibility, and, also, it is possible to remarkably reducethe asymmetry and jitter as well as to remarkably reduce the reflectancedrop and modulation drop at a time of overwriting, in recordingcharacteristics obtained from 4 time speed recording. Furthermore,according to the present invention, upon CAV recording, only controllingthe temporal factors of the top pulse is necessary, and, thus, forexample, it is not necessary to set the top peak pulse power higher thanthe subsequent peak pulse power, or to set the top peak pulse powerlower than the subsequent peak pulse power, or so. As a result, it isnot necessary to complicate a laser driving circuit. Simultaneously, itbecomes not necessary to perform complicated control such as to changethe peak pulse power and/or pulse application interval of the top pulsedepending from a factor such as a separation from the antecedent mark,and also, depending from a factor of each mark length.

Further, the present invention is not limited to the above-describedembodiments, and variations and modifications may be made withoutdeparting from the basic concept of the present invention.

The present application is based on Japanese priority application No.2002-367002, filed on Dec. 18, 2002, the entire contents of which arehereby incorporated by reference.

1. An optical recording method of recording information to a phasechange optical recording medium utilizing change in optical constantcaused by reversible phase change between a crystalline phase and anamorphous phase by controlling power to be applied to the recordingmedium with three values of peak power, erase power and bias power in arecordable range between a minimum linear velocity and a maximum linearvelocity, with alternate application of the peak power and bias power ina pulse manner and with changing the pulse application intervalcontinuously from an inner circumferential part through an outercircumferential part of the recording medium with an intervalproportional to a window width Tw and a fixed interval, comprising thestep of: a) starting a top peak power application interval with a delayfrom a data input pulse signal starting time for a target mark lengthnTw, where n denotes an integer in a range between 3 and 14, withchanging the delay at k/16 times with respect to the window width Twwith changing the same for each linear velocity where k denotes aninteger.
 2. The optical recording method as claimed in claim 1, wherein:as the recording linear velocity is increased, with respect to those atthe minimum linear velocity, a top peak power application starting timeand a tail bias power application ending time are changed in proportionto the window width Tw with changing the proportionality factor withrespect to each linear velocity discretely.
 3. An optical recordingmethod of recording information to a phase change optical recordingmedium utilizing change in optical constant caused by reversible phasechange between a crystalline phase and an amorphous phase by controllingpower to be applied to the recording medium with three values of peakpower, erase power and bias power in a recordable range between aminimum linear velocity and a maximum linear velocity, with alternateapplication of the peak power and bias power in a pulse manner and withchanging the pulse application interval continuously from an innercircumferential part though an outer circumferential part of therecording medium with an interval proportional to a window width Tw anda fixed interval, comprising the step of: a) changing a top peak powerapplication starting time and a tail bias power application ending timein proportion to the window width Tw, with controlling any one thereofwith an interval proportional to the window width Tw determined by afixed factor with respect to the window width Tw independent of thelinear velocity, with respect to those at the minimum linear velocity,upon increase in the recording linear velocity.
 4. The optical recordingmethod as claimed in claim 1, comprising the step of: b) changing thetail bias power application ending time in a range between 0 and thewindow width Tw upon decrease in the linear velocity in case whererecording is mad in a range between the maximum linear velocity and theminimum linear velocity.
 5. The optical recording method as claimed inclaim 2, comprising the step of: b) changing the tail bias powerapplication ending time in a range between 0 and the window width Twupon decrease in the linear velocity in case where recording is made ina range between the maximum linear velocity and the minimum linearvelocity.
 6. The optical recording method as claimed in claim 3,comprising the step of: b) changing the tail bias power applicationending time in a range between 0 and the window width Tw upon decreasein the linear velocity in case where recording is made in a rangebetween the maximum linear velocity and the minimum linear velocity. 7.The optical recording method as claimed in claim 4, wherein: the phasechange optical recording medium applied is characterized in that, bycontinuously applying the erase power which corresponds to more than 20%of the maximum peak power used for recording, the reflectance decreasesform that in a not-yet-recorded state at the maximum linear velocity,while the reflectance does not decreases at the minimum linear velocity.8. The optical recording method as claimed in claim 5, wherein: thephase change optical recording medium applied is characterized in that,by continuously applying the erase power which corresponds to more than20% of the maximum peak power used for recording, the reflectancedecreases from that in a not-yet-recorded state at the maximum linearvelocity, while the reflectance does not decreases at the minimum linearvelocity.
 9. The optical recording method as claimed in claim 6,wherein: the phase change optical recording medium applied ischaracterized in that, by continuously applying the erase power whichcorresponds to more than 20% of the maximum peak power used forrecording, the reflectance decreases from that in a not-yet-recordedstate a the maximum linear velocity, while the reflectance does notdecreases at the minimum linear velocity.
 10. The optical recordingmethod as claimed in claim 1, wherein: the minimum linear velocity isnot less than 1.0 times of a reference linear velocity, while themaximum linear velocity is four times of the reference linear velocity.11. The optical recording method as claimed in claim 2, wherein: theminimum linear velocity is not less than 1.0 times of a reference linearvelocity, while the maximum linear velocity is four times of thereference linear velocity.
 12. The optical recording method as claimedin claim 3, wherein: the minimum linear velocity is not less than 1.0times of a reference linear velocity, while the maximum linear velocityis four times of the reference linear velocity.
 13. The opticalrecording method as claimed in claim 1, wherein: the linear velocity fora case where CAV recording is performed within a data zone to berecorded is determined in a manner in which: for a case where the linearvelocity at the outermost radial position is 4 time speed, the linearvelocity at an intermediate radial position is 2.83 time speed, and thelinear velocity at the innermost radial position is 1.65 time speed; andfor case where the linear velocity at the outermost radial position is2.4 time speed, the linear velocity at the intermediate radial positionis 1.7 time speed, and the linear velocity at the innermost radialposition is 1 time speed.
 14. The optical recording method as claimed inclaim 2, wherein: the linear velocity for a case where CAV recording isperformed within a data zone to be recorded is determined in an mannerin which: for a case where the linear velocity at the outermost radialposition is 4 time speed, the linear velocity at an intermediate radialposition is 2.83 time speed, and the linear velocity at the innermostradial position is 1.65 time speed; and for case where the linearvelocity at the outermost radial position is 2.4 time speed, the linearvelocity at the intermediate radial position is 1.7 time speed, and thelinear velocity at the innermost radial position is 1 time speed. 15.The optical recording method as claimed in claim 3, wherein: the linearvelocity for a case where CAV recording is performed within a data zoneto be recorded is determined in a manner in which: for a case where thelinear velocity at the outermost radial position is 4 time speed, thelinear velocity at an intermediate radial position is 2.83 time speed,and the linear velocity at the innermost radial position is 1.65 timespeed; and for case where the linear velocity at the outmost radialposition is 2.4 time speed, the linear velocity at the intermediateradial position is 1.7 time speed, and the linear velocity at theinnermost radial position is 1 time speed.
 16. The optical recordingmethod as claimed in claim 13, wherein: the linear velocity changescontinuously from the innermost radial position through the outermostradial position while the window width is changed along therewithsubstantially in inverse proportion thereto.
 17. The optical recordingmethod as claimed in claim 14, wherein: the linear velocity changescontinuously from the innermost radial position through the outermostradial position while the window width is changed along therewithsubstantially in inverse proportion thereto.
 18. The optical recordingmethod as claimed in claim 15, wherein: the linear velocity changescontinuously from the innermost radial position through the outermostradial position while the window width is changed along therewithsubstantially in inverse proportion thereto.